This invention pertains to the manufacture of magnetic cores, essentially magnetic tape-wound cores, comprising iron-nickel alloys, which cores are suitable for use with single polarity rectangular voltage pulses and have a high maximum available change of flux-density .DELTA.B of more than 1 T and high pulse permeability. Cost effectiveness is achieved by novel production means and by employing smaller quantities of the more expensive alloy metals, such as nickel. The magnetic alloys may be rolled into thin tapes having a maximum thickness of 0.1 mm and which are shaped as the magnetic core.
In dealing with single polarity pulse transformers, the magnetic core is required to operate between positive residual flux density and positive saturation flux-density. A high available change of flux-density allows transmission of high power pulses. When, simultaneously, pulse permeability is high, it is possible to transmit rectangular voltage pulses without excessive shape distortion using only a few primary windings. In saturable reactors, a high available change of flux-density permits the use of small core cross-sections and a fewer number of windings. This makes possible the necessary current limitation required for some semi-conductor devices during switching to on and off positions.
It is known that by heat treatment and magnetic field treatment of iron-nickel alloys containing more than 50% nickel, it is possible to achieve initial permeabilities of more than 50,000. However, as the result of high residual flux-density B.sub.R these alloys have a low available flux-density change .DELTA.B in working with unipolar voltage pulses. It is also known, that it is possible to increase .DELTA.B by means of an air gap in the magnetic circuit. However, this leads to a simultaneous reduction of the permeability.
Not until the disclosure of Dt-PS No. 15 58 818, herein incorporated by reference, did a material become available which has a high .DELTA.B combined with a favorable initial permeability. In the process disclosed, there is employed an alloy containing nickel-iron-molybdenum in percentages of 61 to 60% nickel, 2 to 4% molybdenum, and the remainder being mainly iron and several deoxidation and processing additives. Tapes of 0.1 to 0.003 mm thickness are made from this alloy and wound as toroidal cores, then heat treated at temperatures from 950.degree. to 1220.degree. C. for 4 to 6 hours followed by a tempering treatment at 400.degree. to 500.degree. C. in a magnetic field axial to the core and transverse to the subsequent direction of the magnetic flux.
The foregoing process is economically disadvantageous since it requires a high nickel content of from 61 to 67 percent and a long tempering treatment of 3 to 5 hours at 400.degree. to 500.degree. C. in a magnetic field to produce the magnetic core.